Re: [PATCH v2 1/2] dhcpv6: Add --dhcpv6-opt with option type table and value parser

On Thu, Jun 18, 2026 at 05:35:28PM +0530, Anshu Kumari wrote:

Introduce the --dhcpv6-opt flag that allows setting arbitrary DHCPv6 options from command-line in the form [--dhcpv6-opt CODE,VALUE].

Add a type lookup table mapping option codes to value types (IPv6, IPv6 list, integer, string, vendor class, length-prefixed string list) and dhcpv6_opt_parse() to convert CLI strings to binary wire format. If the same option code is given more than once, the last value wins.

Link: https://bugs.passt.top/show_bug.cgi?id=192 Signed-off-by: Anshu Kumari --- v2: - Renamed custom_v6opts to dhcpv6_opts, MAX_CUSTOM_DHCPV6_OPTS to MAX_DHCPV6_OPTS. - Dropped val/len from ctx struct. - Moved dhcpv6_add_option() to conf.c as static conf_dhcpv6_option(). - Made dhcpv6_opt_parse() non-static, declared in dhcpv6.h - Omitted explicit [256] from dhcpv6_opt_types[]. - Moved chunk declaration into while block. - Removed redundant !slen check in DHCPV6_OPT_STR case. - All errors in dhcpv6_opt_parse() return -1, removed die() calls. --- conf.c | 60 +++++++++++++++- dhcpv6.c | 209 +++++++++++++++++++++++++++++++++++++++++++++++++++++++ dhcpv6.h | 2 + passt.1 | 31 +++++++++ passt.h | 12 ++++ 5 files changed, 313 insertions(+), 1 deletion(-)

diff --git a/conf.c b/conf.c index cd05adf..3981c1b 100644 --- a/conf.c +++ b/conf.c @@ -47,6 +47,7 @@ #include "lineread.h" #include "isolation.h" #include "log.h" +#include "dhcpv6.h" #include "vhost_user.h" #include "epoll_ctl.h" #include "conf.h" @@ -616,7 +617,8 @@ static void usage(const char *name, FILE *f, int status) " -S, --search LIST Space-separated list, search domains\n" " a single, empty option disables the DNS search list\n" " -H, --hostname NAME Hostname to configure client with\n" - " --fqdn NAME FQDN to configure client with\n"); + " --fqdn NAME FQDN to configure client with\n" + " --dhcpv6-opt CODE,VAL Set DHCPv6 option CODE to VAL\n"); if (strstr(name, "pasta")) FPRINTF(f, " default: don't use any search list\n"); else @@ -884,6 +886,10 @@ static void conf_print(const struct ctx *c) info(" our link-local: %s", inet_ntop(AF_INET6, &c->ip6.our_tap_ll, buf, sizeof(buf))); + for (i = 0; i < c->dhcpv6_opts_count; i++) + info(" v6 option %u: %s", + c->dhcpv6_opts[i].code, + c->dhcpv6_opts[i].str);

dns6: for (i = 0; i < ARRAY_SIZE(c->ip6.dns); i++) { @@ -1150,6 +1156,41 @@ static void conf_sock_listen(const struct ctx *c) die_perror("Couldn't add configuration socket to epoll"); }

+/** + * conf_dhcpv6_option() - Set value for a DHCPv6 option in configuration + * @c: Execution context + * @code: DHCPv6 option code + * @val_str: Value string from command line + */ +static void conf_dhcpv6_option(struct ctx *c, uint16_t code, + const char *val_str) +{ + uint8_t tmp[255]; + int idx; + + if (dhcpv6_opt_parse(code, val_str, tmp, sizeof(tmp)) < 0) + die("Invalid value for DHCPv6 option %u: %s", code, val_str);

As for DHCPv4, I wonder if we can avoid double parsing each option. I realise the data structures in dhcpv6.c are different from those in dhcp.c, so it might not reasonable here, even if it is there.

+ for (idx = 0; idx < c->dhcpv6_opts_count; idx++) { + if (c->dhcpv6_opts[idx].code == code) + break; + } + + if (idx == c->dhcpv6_opts_count) { + if (c->dhcpv6_opts_count >= MAX_DHCPV6_OPTS) + die("Too many --dhcpv6-opt entries (max %d)", + MAX_DHCPV6_OPTS); + c->dhcpv6_opts_count++; + } + + c->dhcpv6_opts[idx].code = code; + + if (snprintf_check(c->dhcpv6_opts[idx].str, + sizeof(c->dhcpv6_opts[0].str), + "%s", val_str)) + die("DHCPv6 option value too long: %s", val_str); +} + /** * conf() - Process command-line arguments and set configuration * @c: Execution context @@ -1233,6 +1274,7 @@ void conf(struct ctx *c, int argc, char **argv) {"migrate-no-linger", no_argument, NULL, 30 }, {"stats", required_argument, NULL, 31 }, {"conf-path", required_argument, NULL, 'c' }, + {"dhcpv6-opt", required_argument, NULL, 35 }, { 0 }, }; const char *optstring = "+dqfel:hs:c:F:I:p:P:m:a:n:M:g:i:o:D:S:H:461t:u:T:U:"; @@ -1248,10 +1290,13 @@ void conf(struct ctx *c, int argc, char **argv) uint8_t prefix_len_from_opt = 0; unsigned int ifi4 = 0, ifi6 = 0; const char *logfile = NULL; + unsigned long v6optcode; char *runas = NULL; size_t logsize = 0; + const char *comma; long fd_tap_opt; int name, ret; + char *end; uid_t uid; gid_t gid;

@@ -1467,6 +1512,19 @@ void conf(struct ctx *c, int argc, char **argv) die("Can't display statistics if not running in foreground"); c->stats = strtol(optarg, NULL, 0); break; + case 35: + comma = strchr(optarg, ','); + if (!comma) + die("--dhcpv6-opt requires CODE,VALUE format"); + + errno = 0; + v6optcode = strtoul(optarg, &end, 0); + if (end != comma || errno || v6optcode < 1) + die("Invalid DHCPv6 option code: %s", + optarg); + + conf_dhcpv6_option(c, v6optcode, comma + 1); + break; case 'd': c->debug = 1; c->quiet = 0; diff --git a/dhcpv6.c b/dhcpv6.c index 97c04e2..1e1dd0d 100644 --- a/dhcpv6.c +++ b/dhcpv6.c @@ -25,6 +25,7 @@ #include #include #include +#include

#include "packet.h" #include "util.h" @@ -278,6 +279,214 @@ static struct resp_not_on_link_t { { 0, }, };

+/** + * enum dhcpv6_opt_type - DHCPv6 option value types + * @DHCPV6_OPT_NONE: Unsupported or unknown option + * @DHCPV6_OPT_STR: Variable-length string + * @DHCPV6_OPT_IPV6: Single IPv6 address + * @DHCPV6_OPT_IPV6_LIST: Multiple IPv6 addresses, comma-separated + * @DHCPV6_OPT_INT8: Unsigned 8-bit integer + * @DHCPV6_OPT_INT16: Unsigned 16-bit integer + * @DHCPV6_OPT_INT32: Unsigned 32-bit integer + * @DHCPV6_OPT_VENDOR_CLASS: Enterprise number + length-prefixed data + * @DHCPV6_OPT_LEN_STR_LIST: Length-prefixed string list + */ +enum dhcpv6_opt_type { + DHCPV6_OPT_NONE, + DHCPV6_OPT_STR, + DHCPV6_OPT_IPV6, + DHCPV6_OPT_IPV6_LIST, + DHCPV6_OPT_INT8, + DHCPV6_OPT_INT16, + DHCPV6_OPT_INT32, + DHCPV6_OPT_VENDOR_CLASS, + DHCPV6_OPT_LEN_STR_LIST, +}; + +/** + * dhcpv6_opt_types - Maps DHCPv6 option code to value type, indexed by code + * RFC 8415 Options: 7, 15, 16, 17, 32, 82, 83 + * RFC 5970 Options: 59, 60 + * RFC 4075 Options: 31 + */ +static const enum dhcpv6_opt_type dhcpv6_opt_types[] = { + [7] = DHCPV6_OPT_INT8, /* Preference */ + [15] = DHCPV6_OPT_LEN_STR_LIST, /* User Class */ + [16] = DHCPV6_OPT_VENDOR_CLASS, /* Vendor Class */ + [17] = DHCPV6_OPT_VENDOR_CLASS, /* Vendor Opts */ + [31] = DHCPV6_OPT_IPV6_LIST, /* SNTP Servers */ + [32] = DHCPV6_OPT_INT32, /* Information Refresh Time */ + [59] = DHCPV6_OPT_STR, /* Boot File URL */ + [60] = DHCPV6_OPT_LEN_STR_LIST, /* Boot File Params */ + [82] = DHCPV6_OPT_INT32, /* SOL_MAX_RT */ + [83] = DHCPV6_OPT_INT32, /* INF_MAX_RT */ +}; + +/** + * dhcpv6_opt_parse() - Parse a DHCPv6 option value string into binary + * @code: DHCPv6 option code + * @str: Value string from command line + * @buf: Output buffer for binary value + * @buf_len: Size of output buffer + * + * Return: number of bytes written to @buf, or -1 on error + */ +int dhcpv6_opt_parse(uint16_t code, const char *str, + uint8_t *buf, size_t buf_len) +{ + enum dhcpv6_opt_type type; + unsigned long val; + unsigned int i; + uint8_t width; + size_t slen; + char *end; + int len; + + if (!*str) + return -1; + + if (code >= ARRAY_SIZE(dhcpv6_opt_types)) + return -1; + + type = dhcpv6_opt_types[code]; + + switch (type) {

A number of these types result in identical parsing to DHCPv4. Could we have a unified parser function? Obviously things like IPv4 address and IPv6 address would need different types, but we should be able to share at least the integer and string code.

+ case DHCPV6_OPT_NONE: + return -1; + case DHCPV6_OPT_IPV6: + case DHCPV6_OPT_IPV6_LIST: + len = 0; + + while (*str) { + char chunk[INET6_ADDRSTRLEN]; + size_t clen; + + clen = strcspn(str, ","); + if (!clen || clen >= sizeof(chunk)) + return -1; + + if (len + (int)sizeof(struct in6_addr) > (int)buf_len) + return -1; + + memcpy(chunk, str, clen); + chunk[clen] = '\0'; + + if (inet_pton(AF_INET6, chunk, buf + len) != 1) + return -1; + + len += sizeof(struct in6_addr); + + if (type == DHCPV6_OPT_IPV6) { + if (str[clen] == ',') + return -1; + break; + } + + str += clen + (str[clen] == ','); + } + + if (!len) + return -1; + + return len; + case DHCPV6_OPT_INT8: + case DHCPV6_OPT_INT16: + case DHCPV6_OPT_INT32: + if (type == DHCPV6_OPT_INT8) + width = 1; + else if (type == DHCPV6_OPT_INT16) + width = 2; + else + width = 4; + + if (buf_len < width) + return -1; + + errno = 0; + val = strtoul(str, &end, 0); + + if (*end || errno || val >= (1ULL << (width * 8))) + return -1; + + for (i = width; i > 0; i--) { + buf[i - 1] = val & 0xff; + val >>= 8; + } + + return width; + case DHCPV6_OPT_STR: + slen = strlen(str); + + if (slen >= buf_len) + return -1; + + memcpy(buf, str, slen); + + return slen; + case DHCPV6_OPT_VENDOR_CLASS: { + const char *colon; + uint32_t ent; + + colon = strchr(str, ':'); + if (!colon) + return -1; + + errno = 0; + val = strtoul(str, &end, 0); + if (end != colon || errno || val > UINT32_MAX) + return -1; + + slen = strlen(colon + 1); + if (!slen) + return -1; + + len = sizeof(uint32_t) + sizeof(uint16_t) + slen; + if ((size_t)len > buf_len) + return -1; + + ent = htonl(val); + memcpy(buf, &ent, sizeof(ent)); + + buf[4] = slen >> 8; + buf[5] = slen & 0xff; + + memcpy(buf + sizeof(uint32_t) + sizeof(uint16_t), + colon + 1, slen); + + return len; + } + case DHCPV6_OPT_LEN_STR_LIST: + len = 0; + + while (*str) { + slen = strcspn(str, ","); + if (!slen) + return -1; + + if (len + (int)(sizeof(uint16_t) + slen) > (int)buf_len) + return -1; + + buf[len] = slen >> 8; + buf[len + 1] = slen & 0xff; + len += sizeof(uint16_t); + + memcpy(buf + len, str, slen); + len += slen; + + str += slen; + if (*str == ',') + str++; + } + + if (!len) + return -1; + + return len; + } + + return -1; +} + /** * dhcpv6_opt() - Get option from DHCPv6 message * @data: Buffer with options, set to matching option on return diff --git a/dhcpv6.h b/dhcpv6.h index c706dfd..2da1c76 100644 --- a/dhcpv6.h +++ b/dhcpv6.h @@ -9,5 +9,7 @@ int dhcpv6(struct ctx *c, struct iov_tail *data, struct in6_addr *saddr, struct in6_addr *daddr); void dhcpv6_init(const struct ctx *c); +int dhcpv6_opt_parse(uint16_t code, const char *str, + uint8_t *buf, size_t buf_len);

#endif /* DHCPV6_H */ diff --git a/passt.1 b/passt.1 index 908fd4a..0f771cb 100644 --- a/passt.1 +++ b/passt.1 @@ -430,6 +430,37 @@ Send \fIname\fR as DHCP option 12 (hostname). FQDN to configure the client with. Send \fIname\fR as Client FQDN: DHCP option 81 and DHCPv6 option 39.

+.TP +.BR \-\-dhcpv6-opt " " \fICODE\fR,\fIVALUE\fR +Set DHCPv6 option \fICODE\fR to \fIVALUE\fR. The value format depends +on the option type and is determined automatically from the option code. +Multiple IPv6 addresses are comma-separated. +This option can be specified multiple times. If the same option code is +given more than once, the last value wins. +.RS +.TP +.B String options +59 (Boot File URL, RFC 5970) +.TP +.B Length-prefixed string list options (comma-separated entries) +15 (User Class, RFC 8415), 60 (Boot File Params, RFC 5970). +Each comma-separated entry is encoded with a 2-byte length prefix. +Example: \fB\-\-dhcpv6-opt 15,class1,class2\fR. +.TP +.B Vendor class options (ENTERPRISE:DATA format) +16 (Vendor Class, RFC 8415), 17 (Vendor-specific Info, RFC 8415). +VALUE is \fIENTERPRISE\fR:\fIDATA\fR where \fIENTERPRISE\fR is the IANA +Private Enterprise Number and \fIDATA\fR is the vendor class string. +Example: \fB\-\-dhcpv6-opt 16,0:HTTPClient\fR for UEFI HTTP Boot. +.TP +.B IPv6 address list options (comma-separated) +31 (SNTP Servers) +.TP +.B Integer options +7 (Preference, 8-bit), 32 (Information Refresh Time, 32-bit), +82 (SOL_MAX_RT, 32-bit), 83 (INF_MAX_RT, 32-bit) +.RE + .TP .BR \-t ", " \-\-tcp-ports " " \fIspec Configure TCP port forwarding to guest or namespace. \fIspec\fR can be one of: diff --git a/passt.h b/passt.h index 3a07294..8f4ddef 100644 --- a/passt.h +++ b/passt.h @@ -182,6 +182,10 @@ struct ip6_ctx { * @dns_search: DNS search list * @hostname: Guest hostname * @fqdn: Guest FQDN + * @dhcpv6_opts: User-specified DHCPv6 options from --dhcpv6-opt + * @dhcpv6_opts.code: DHCPv6 option code + * @dhcpv6_opts.str: String value from command line + * @dhcpv6_opts_count: Number of entries in @dhcpv6_opts * @ifi6: Template interface for IPv6, -1: none, 0: IPv6 disabled * @ip6: IPv6 configuration * @pasta_ifn: Name of namespace interface for pasta @@ -264,6 +268,14 @@ struct ctx { char hostname[PASST_MAXDNAME]; char fqdn[PASST_MAXDNAME];

+#define MAX_DHCPV6_OPTS 32 + + struct { + uint16_t code; + char str[255]; + } dhcpv6_opts[MAX_DHCPV6_OPTS]; + int dhcpv6_opts_count; + int ifi6; struct ip6_ctx ip6;

-- 2.54.0

-- David Gibson (he or they) | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you, not the other way | around. http://www.ozlabs.org/~dgibson